The present invention relates to surge protection in a power distribution system. More particularly, the present invention relates to a surge protector which is economical, reliable, and flexible, and a method for making the same.
Electrical components can be severely damaged by electrical surges, and there are many types of surge suppressors which have been designed to address this problem. One example of a known surge suppressor is disclosed in U.S. Pat. No. 4,809,124 as a high energy, low voltage surge arrestor. The surge arrestor of the '124 patent discloses an embodiment which includes a thin disk of metal oxide varistor (MOV) material having a circular periphery and opposite planar external surfaces. The planar external surfaces are coated with a highly conductive material, and two electrodes are brazed or clamped to the metallized external surfaces, the clamped arranged being preferred when very high currents are anticipated. Each electrode is in the form of a generally circular flat plate with two terminal lugs projecting radially from the electrode body on diametrically-opposed sides of the electrode body. The electrode disclosed in the '124 patent is suitable for use in the circuit shown in FIG. 4 thereof, where two spaced-apart conductors interconnect a source and a load, one conductor connecting an upper terminal of the source to an upper terminal of the load, and the other conductor connecting a lower terminal of the load to a lower terminal of the source. The surge arrester disclosed in the '124 patent is, in effect, connected across the first and second conductors in parallel with the load.
FIG. 1 is an example of using surge protectors to provide multiple "modes of protection" in an electrical distribution system having three phases A, B, and C, a neutral N and a ground G. In FIG. 1, surge protection is provided between the neutral N and each of phases A, B, and C, as well as ground G. Thus, in this embodiment, four modes of protection are provided. Additional modes of protection may be desirable and achievable. For example, seven modes of protection can be achieved by providing surge protection between the neutral N and each of phases A, B and C, between ground G and each of phases A, B and C, and between neutral N and ground G as shown in FIG. 5. Additional modes of protection can be achieved by providing surge protection between each of the phases A, B, and C.
The surge arrester of the '124 patent, and other known surge arresters, suffer from numerous drawbacks. First, they can be expensive to produce and assemble because they are typically housed in a housing using numerous machined textolite pieces. Second, the devices are not readily adaptable to provide more than four modes of protection, because the interconnections required to achieve additional modes of protection are not easily and reliably made. Third, the heat transfer characteristics of conventional surge protectors (that is, their ability to dissipate heat following a surge event) are insufficient and make it difficult to reduce size and cost.
Fourth, connections within the surge protectors are typically cumbersome, adding inductance and increasing the transient voltage during a surge event. It would be desirable to provide a low cost, relatively small surge protector with reliable connections. Such a surge protector should also provide flexibility to accommodate different connection options and different modes of protection. It would further be desirable for such a surge protector to be adaptable to allow modifications to reduce cost for light duty applications, or to allow modifications to increase the surge rating for heavier duty applications with minor changes. It would also be desirable for a surge protector to have improved heat transfer characteristics.
It would also be desirable to minimize the interconnection lead lengths, thereby reducing the surge impedance and induced voltages during transient events. Known surge protectors do not provide these and other desirable features.